The present invention relates to a winding-in device for safety belts in motor vehicles, of the kind in which said device has a shaft, rotatably mounted in a housing of the device, to receive the safety belt, which in withdrawable, and having locking means by which the shaft is locked against further rotation in the withdrawal direction when a predetermined limiting level of angular acceleration is exceeded, and further having an inertia body, rotatable on and with the shaft, which, when the said limiting level is exceeded, lags behind the rotary movement of the shaft in opposition to the effect of spring means which connect it to the shaft, so that, in so doing, it can bring at least one locking pawl, which is mounted to pivot in a flange on the shaft, into engagement with a ring of teeth secured to the housing via a cam track. Hereinafter such a device will be referred to as "of the kind described".
In the case of known winding-in devices, a distinction can, in principle, be made between two different kinds of direct acting locking means. With one kind the locking means respond, when the speed of rotation of the shaft exceeds a specified value, by for example causing a locking member connected to the shaft to move outwards under the promoting of the centrifugal force which acts on it and allowing to come it into engagement with a fixed ring of teeth or a fixed projection. The disadvantage of this design lies above all in the fact that the locking speed may be reached as soon as the belt begins to be pulled out or even if the person held in the belt bends forward fairly quickly without being caused to do so by an accident, thus causing the lock to function unnecessarily.
A change has therefore already been made to allow the locking means to operate in response to the angular acceleration of the shaft carrying the belt, a specific critical value being set above which the lock comes into action. This would be the case if, say, the belt were pulled out with a jerk, whereas otherwise the belt can, in principle, be pulled out from the shaft at any desired speed without locking taking place.
Belt reels fitted with locking means of this kind have for example an inertia body rotatably mounted on the shaft which may be connected to the shaft by a traction spring and which in normal operation travels with the shaft in the same direction of rotation. If however the shaft is turned with an angular acceleration which exceeds the preset limiting value, the inertia body lags behind the shaft in opposition to the traction spring which is pulling it along with the shaft. The relative rotation which thus occurs is made use of to pivot a locking pawl about a mounting point, via levers, linkages, gears or the like, until a locking tooth on the pawl can come into positive engagement with a ring of teeth secured to the housing and can prevent further rotation of the shaft.
It is an object of the invention to improve winding-in devices of the kind described so that they shall be easy to assemble, reliable in operation and compact in construction.